The field of the invention relates to coupling devices for coupling a lens to a single mode optical fiber. The field of the invention further relates to medical imaging devices incorporating such coupling devices.
Recently, substantial attention has been directed toward the development and implementation of imaging systems that provide optical feedback to the clinician. For example, optical feedback systems have been employed in intraluminal, intracavity, intravascular, and intracardiac treatment and diagnosis of medical conditions utilizing minimally invasive procedures. As one common example, these procedures are typically performed using imaging and treatment catheters that are inserted percutaneously into the body and into an accessible vessel of the vascular system at a site remote from a region of the body to be diagnosed and/or treated. The catheter can be equipped with an imaging device, typically located at the distal end thereof, that is used to locate and diagnose a diseased portion of the body.
In the past, medical imaging devices typically obtained images using an ultrasound imaging system. More recently, however, a growing interest has arisen in imaging devices employing optical coherence tomography (OCT). OCT is analogous to traditional ultrasound imaging techniques in that the technique measures back-reflected light rather than acoustical waves. OCT uses low coherence interferometry to perform high resolution, cross-sectional imaging of biological structures. OCT is a promising imaging method, in part, because OCT has a higher resolution than traditional ultrasound imaging techniques.
OCT devices are typically used in connection with one or more optical fibers in conjunction with an interventional device. The one or more optical fibers are attached to an imaging console that displays an image or a processor that interprets data. Potential applications of such systems include the stationary tissue spectroscopy of polyps and other mucosal tissue, linear scans of various portions of the human anatomy, and cross-sectional views of tubular vessels such as arteries, the gastro-intestinal tract, urological structures, the biliary tree, and neurological vessels. Of course, the examples mentioned above are only illustrative, as OCT imaging techniques can be used in applications other than those specifically set forth.
Procedures such as tissue spectroscopy typically utilize an endoscope, cytoscope, colonoscope, or sigmoidoscope for direct visual feedback. The scope typically helps direct a biopsy device, a light source, and an optical path for visual guidance. Other procedures involving optical feedback use guidewires. Still others use trocars for direct access to some parts of the anatomy, such as the breast for breast biopsies, and other areas inaccessible through an orifice.
In medical imaging devices using light as the radiation source, single mode optical fibers are often employed. In such applications, light from a source must be coupled into a single mode optical fiber, which requires optics to focus the light in a very small diameter. The transmitting area or core of an optical fiber is then aligned with the focused beam of light typically using multi-axis positioners with optical feedback systems. The lens is locked into place using epoxy or solder. Many factors affect the efficiency of coupling light into optical fibers, but one of the most critical is the accuracy of the alignment of the fiber axis with the optical axis of the lens system.
After light is coupled into a fiber, it is transported with relatively low losses within the single mode optical fiber to the desired location. When the optical fiber is terminated, light rays exiting the fiber are divergent, exiting the fiber within a narrow cone angle. The exiting light rays are then bent into the desired shape using one or more lenses. In prior art designs, various lens systems have been used to focus or collimate the light. Conventional optics sometimes require multiple lenses, each needing its own precision holder or positioning system. GRadient INdex (GRIN) lenses reduce the number of lenses required by bending the path of light within the lens. However, GRIN lenses also require complex and expensive positioning systems to provide efficient coupling into single mode optical fiber.
Conventional optical fibers utilize a stepped index of refraction to confine light within the core. The core, or area of the fiber that actually carries the light, is constructed with a lower index of refraction and the cladding (the outer glass layer) is made of a higher index of refraction. This causes light rays straying from the core to be reflected back into the core of the optical fiber with little loss. The core of single mode optical fiber ranges in size from about 3 microns up to 9 microns diameter.
Another type of optical fiber readily available is graded refractive index fiber. This fiber has no discrete core and cladding, rather a radially graded index of refraction causes the light to be bent back towards the center of the fiber, resulting in a sinusoidal path. For very short lengths, this fiber bends light exactly the same way the GRIN rod lenses do, so it can also be used as a lens. The advantages of using graded index fiber as a lens are, graded index fiber is available in the same diameter as single mode optical fibers, and they are extremely inexpensive.
In the field of minimally invasive surgery, catheters are often required with outer diameters that are limited to less than one millimeter. This restricts the use of conventional optics and in some cases even GRIN rod lenses due to the tiny diameters needed. When single mode optical fibers are used in these devices, there frequently is a need for focusing or collimating optics at the tip, or distal end of the device. Since the diameter into which light must be focused into is around 5 microns (0.0002"), aligning a lens with the required precision without the use of active alignment systems is difficult or impossible. A system is needed that eliminates the cost and complexity of this task.
In medical imaging devices incorporating single mode optical fiber, it is often desirable to rotate the optical fiber and/or any associated optical components to sweep the beam across a region of the body, i.e., the interior of an artery. Portions of the beam are reflected back through the use of optical lenses and reflectors. A separate analyzing device analyzes the data in the single mode optical fiber. By acquiring the rotational positioning of the optical fiber, an optical map can then be reconstructed, through mathematical algorithms, to produce detailed imaging data of the swept region. This imaging data can be displayed on a monitor for example, to provide real-time, or near real-time imaging.
One particular type of device that rotates a rotatable optical fiber is disclosed in U.S. Pat. No. 5,872,879. This patent is incorporated by reference as if set forth fully herein. Generally, a fiber-optic motor assembly is used to rotate the optical fiber within an insertion device (i.e., catheter, endoscope, guidewire, trocar, or the like).
When single mode optical fibers are employed, it is very difficult to align the optical lens with the single mode optical fiber with accuracy and precision. While time-consuming optical feedback-based systems are available to align single mode optical fibers with optical lenses, these devices and systems are complex and costly. Accordingly, there is a need for a compact, low cost optical lens system that permits focusing, collimating, and coupling into a single mode optical fiber.